I don't know :)

The smartest people I know say I don't know all the time as one can never know everything so why do people bs and prevaricate when faced with something unknowable as unknowables reside everywhere from knowing how many galaxies are there in the universe to how many grains of sand reside on the local beach. One never knows do one? The uncertainty principle rules and so does the honest statement I don't know as truth never sells, it's clear and concise so saying I  don't know is something I say all the time and I'm in good company as Einstein's and Feynman's mantra was Question everything, a philosophy one should live by without question.

Throughout the process of interviewing some of the most experienced candidates in the field, Apple looks beyond knowledge. Instead, it is in search of those whose work can flourish in a fast-paced and energetic environment that puts innovation at the forefront and evolution at the core. 

To find such a candidate in the course of an interview, there's one three-word sentence that very few are willing to say that separates the well-qualified candidates from the best-qualified candidates. It's those who are willing to say they don't know something, or simply put, those who are willing to say: 

"I don't know."

Works for me. :)